An important aspect of adjustment in adolescence is the nature and quality of social functioning, which includes relationships with parents, friends, and romantic partners as well as general functioning in the peer group. A key influence on adaptive or maladaptive social functioning across the life course is thought to be the security or insecurity of attachment. With a few notable exceptions, longitudinal studies of social functioning or studies attempting to link attachment quality with social functioning have followed a relatively small number of participants for only a few years. Key questions regarding sources of continuity and change in social functioning over time, the predictive significance of early vs. later attachment quality, and the role of contextual factors (e.g., significant life changes in the family) require long-term longitudinal data on a large number of participants. The answers to these questions are significant for understanding developmental pathways to optimal healthy functioning in adulthood. The primary purpose of the proposed study is to investigate pathways to the nature and quality of social functioning and attachment from infancy to late adolescence. We propose to take advantage of an unparalleled opportunity to address these questions by enrolling the existing longitudinal NICHD Study of Early Child Care and Youth Development (SECCYD) sample. The 1,000 SECCYD participants have been followed from infancy through mid-adolescence. We plan to assess this cohort at age 17.5 years and to add multiple measures of attachment quality, social functioning, and contextual factors, which we will collect via interviews and web-based questionnaires. Parents, best friends, and romantic partners of the study adolescents also will participate. The specific aims are (i) to identify developmental pathways to adaptive and maladaptive social functioning in late adolescence;(2) to evaluate the relations among relationships from early childhood to late adolescence and the relative strength of the associations between the quality of specific relationships and attachment quality;and (3) to evaluate stability and change in attachment, and in attachment in relation to social functioning, from infancy to late adolescence. A secondary aim is (4) to address methodological issues in attachment research. Adolescence is a fundamentally important period for the study of both positive and problematic development and behavior. In this period, experiences set the stage for functioning in adulthood, as individuals sort into trajectories of risk and opportunity that become increasingly difficult to alter. Thus, understanding developmental pathways to adaptive or maladaptive patterns of social behavior and relationships and the processes influencing developmental continuity and change in social functioning will provide fundamental knowledge that is relevant to public health as .well as theory.